linux-kernel - Re: [PATCH] KVM: SVM: Use a separate vmcb for the nested L2 guest

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Message-ID: <c3645ce6-5110-9bcc-450d-69e3f6aabc6a@redhat.com>
Date:   Tue, 22 Sep 2020 17:02:46 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Cathy Avery <cavery@...hat.com>, Wei Huang <wei.huang2@....com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com
Subject: Re: [PATCH] KVM: SVM: Use a separate vmcb for the nested L2 guest

On 21/09/20 16:07, Cathy Avery wrote:
>>>   -    if (npt_enabled)
>>> -        svm->vmcb->save.cr3 = hsave->save.cr3;
>>> +    if (!npt_enabled)
>>> +        svm->vmcb01->save.cr3 = kvm_read_cr3(&svm->vcpu);
>> Does this mean the original code is missing the following?
>>
>>          else
>>         svm->vmcb01->save.cr3 = kvm_read_cr3(&svm->vcpu);
> No it means I made an assumption here. I'll look at this again.

This should not be needed, nested_svm_load_cr3's call to kvm_init_mmu
should write to svm->vmcb->save.cr3.

>>>
>>> +    unsigned long vmcb01_pa;
>> Any reason that vmcb01_pa can't be placed in "struct vcpu_svm" below, along
>> with vmcb01?
> I just grouped it with the other nesting components. I can move it.

Please do it, vmcb01 is not part of nesting.

>     static inline struct vmcb *get_host_vmcb(struct vcpu_svm *svm)
>   {
> -    if (is_guest_mode(&svm->vcpu))
> -        return svm->nested.hsave;
> -    else
> -        return svm->vmcb;
> +    return svm->vmcb01; 

You can remove the function altogether (in a second patch).

Paolo